Kurdish soldiers, also known as pesh merga, study a map near the front line on the outskirts of the town of Makhmour, Iraq. The pesh merga have been fighting Islamic State extremists, whose momentum appears to have slowed somewhat. (Sebastian Meyer/For The Washington Post)

OUTSIDE MAKHMOUR, Iraq — On the newest front line of the expanding war being waged by Sunni militants for control of the Middle East, the juggernaut of the Islamic State’s advance appeared Saturday to have slowed, at least for now.

Buoyed by U.S. airstrikes the previous day, Kurdish pesh merga fighters said they pushed back an attempt by the extremists to overrun one of their artillery positions on the northern edge of the dust-blown town of Makhmour, south of Irbil. Makhmour was seized by Islamic State fighters Thursday.

At the same time, however, commanders said Islamic State fighters had begun to return to positions that U.S. airstrikes had forced them to flee — a reminder that the so-far limited intervention may represent only the beginning of what President Obama warned Saturday could be a long campaign. Hours later, the U.S. military announced it had carried out four more airstrikes, in the Sinjar area farther west.

The Islamic State boasted in a video of its newest conquests, including Iraq’s biggest hydroelectric dam, outside Mosul. If breached, the dam would inundate towns and villages along the Tigris river and unleash flooding as far south as Baghdad.

The renegade al-Qaeda force is also reported to have made advances elsewhere across the vast stretch of territory it controls, in the Iraqi province of Anbar, in Kirkuk and in the eastern Syrian province of Hasakah.

Their spirits bolstered by the U.S. intervention, Kurdish forces began to regroup after their rout in the past week, in which they retreated from a string of towns and villages. Tens of thousands of civilians, including Christians and Yazidis, were displaced.

As the sound of outgoing artillery and heavy machine-gun fire rang out across the undulating fields outside Makhmour, trucks bearing fresh supplies of ammunition and SUVs carrying uniformed officers hurtled to reinforce the front lines.

Hundreds of volunteers drawn from all over the Kurdistan region also streamed toward the battle, clutching ancient rifles and wearing the ballooning pants and waistcoats traditional to Kurdish culture.

The first of the three U.S. airstrikes had taken out an Islamic State artillery position nearby, and pesh merga commanders said they sensed the militants had been chastened by the attack.

“This power they had before, this momentum — we don’t see it now,” said Col. Mohsin Avdal, who sat poring over maps on an ammunition box beside a pile of several dozen newly arrived 107mm rockets. They were delivered, he said, from stocks the pesh merga already owned.

But there was little indication the airstrikes had done much more than slow the militant blitz through Iraq and Syria, where Islamic State forces now govern a vast swath of territory in the name of their self-proclaimed caliphate.

Pesh merga commanders said they had no immediate plans to attempt to push back the militants but rather were under orders to consolidate the positions they now hold.

“We are not moving forward. We are staying put. We are ready and we are strong,” said Mohammed Mohsin, a brigadier general who has come out of retirement to oversee the reinforcement of another front-line checkpoint outside the town of Kalak, east of Irbil.

“But they are really strong,” he added, referring to Islamic State forces. “Everything the Americans sold to the Iraqi army, they have it now.”

The two other American strikes hit an Islamic State mortar position and a convoy a little more than a mile beyond the checkpoint, deterring an attempt by the militants to advance on the position, Mohsin said. Kurdish fighters who visited the site shortly after the strike found the remains of four U.S.-made Humvees that had been captured from the Iraqi army and the bodies of 13 Islamic State fighters. It was all that remained of a convoy that had attempted to advance on the Kurdish position.

But the Kurdish fighters lacked the resources to hold the location and were ordered back to their base at Kalak, Mohsin said.

Later in the day, Islamic State fighters were seen returning to the area, according to Brig. Gen. Azad Hawezi, who commands forces in the area.

“They are bringing new people and more of those weapons they captured from the Iraqi army,” he said.

“They have American weapons, and they have American vehicles,” he added. “Obviously, they are strong.”

Unless the pesh merga are able to make advances, “it would seem likely that further [Islamic State] progress or escalated U.S. airstrikes are the only eventualities,” said Charles Lister of the Brookings Doha Center in Qatar. “Airstrikes by themselves can only ever represent a potential temporary fix against a force like the Islamic State.”

The United States has promised to send arms and ammunition, but the pesh merga say they would need a massive influx to be able to make real gains against the militants. Their forces are stretched thin along a 650-mile front line, and although Kurdish civilians swarmed to offer their services as reinforcements, their utility was in question.

“We have guns, but we need heavy weapons,” said Abdul Aziz Ibrahim, 52, a farmer who fled the advance of the Islamic State on Makhmour overnight Thursday and has returned to join the fight as a volunteer, armed with an aged AK-47 borrowed from a relative.

“The pesh merga ran out of ammunition. There were too many of them,” he said, describing how the entire town fled within minutes of the first shell fired by Islamic State fighters. “Only the American Air Force can save us.”

Other Kurdish civilians had bought guns, flak jackets and helmets on the open market, making their way to the front lines from as far afield as the Iranian border.

Though enthusiastic, the volunteers seemed only to be getting in the way. They milled around checkpoints, taking turns to peer through binoculars at the front line about a mile away whenever an explosion thundered through the air, and they clogged roads the real fighters were using to ferry supplies and men to the front.

Lt. Col. Abdul Aziz Ali Mustafa, who was directing the deployment of fighters on the outskirts of Makhmour, predicted a long fight.

“All we can do is defend our territory and prepare to die, until someone finds a solution,” he said. “This is a big problem, involving all the Arab world. It is not something we can solve.”

Loveday Morris in Baghdad contributed to this report.

Liz Sly is the Post’s Beirut bureau chief. She has spent more than 15 years covering the Middle East, including the Iraq war. Other postings include Africa, China and Afghanistan.

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